For some reason, in Excel 2009, all of my column headers are now Numbers
rather than letters. Is there a setting within Excel or a fast-key that
automatically changed this without me looking?

Did you mean Excel 2003? If yers, then read on...

To change this behavior, follow these steps:

1. Start Microsoft Excel.
2. On the Tools menu, click Options.
3. Click the General tab.
4. Under Settings, click to clear the R1C1 reference style check box
(upper-left corner), and then click OK.

If you select the R1C1 reference style check box, Excel changes the
reference style of both row and column headings, and cell references from the
A1 style to the R1C1 style.

In Excel 2007
Office Button-Excel Options-FORMULAS-WORKING WITH FORMULAS
click to clear the R1C1 reference style check box
"DaveM" wrote:

For some reason, in Excel 2009, all of my column headers are now Numbers
rather than letters. Is there a setting within Excel or a fast-key that
automatically changed this without me looking?